The invention also relates to a construction kit and an assembly of suppression elements and an apparatus for extracting minerals.
Suppression elements for vortex vibrations are, for instance, known from the offshore industry as so-called ‘Vortex Induced Vibration Strakes’ or ‘VIV Strakes’. Such suppression elements are used on, for instance, offshore drilling platforms to reduce the forces exerted by the water on the pipeline running from the platform to the oil well or a so-called ‘off-loading vessel’. Owing to the flow of the water, the pipeline experiences a force, on the one hand because the water, because of flow, exerts a force on the upstream front side of the line, and on the other hand because on the downstream back side vortices arise, by which a suction force is exerted on the back side. The vortices on the back side can also cause vibrations in the pipelines. The suppression elements intend to reduce these vortices and are often provided around the pipeline from the water level to a depth of 300-500 feet since in this area the flow of the seawater is greatest.
The known suppression elements, such as, for instance, described in U.S. Pat. Nos. 5,421,413 and 6,347,911, are designed as a tube or casing for the pipeline with one or more radially projecting fins or ‘vanes’. Several tubes are longitudinally placed in line with each other so as to obtain an elongate suppression system. Often these vanes are triangular in cross-section and extend spirally in the longitudinal direction of the pipeline.
A drawback of the known suppression elements is that the manufacture thereof is complicated and expensive. U.S. Pat. No. 6,347,911, for instance, discloses a method for manufacturing the suppression element, wherein first a flat parallelogram-shaped plate is manufactured with strips, which are then turned into a tubular form.